#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
using namespace std;

int main()
{
	int N = 0;
	int K = 0;
	int M = 0;
	scanf("%d %d %d", &N, &K, &M);

	int rest = 0;
	rest = N - K * M;
	printf("%d", rest);

	return 0;
}
